Certain mechanical devices include a rotatable component which following a given rotative movement thereof from a normally stopped position, is intended to be returned to said normally stopped position by a suitable means such as a spring, the return travel often being required to be rapidly effected. To absorb such rapid return travel momentum, the rotatable component has in many instances been operatively connected to a damping device such as a fluid operated shock absorber. Such form of momentum damping is not always effective to produce complete stopping of the rotatable component at its normally stopped position so that as a consequence, the rotatable component can override such normally stopped position a distance, return back past said position and continue to oscillate thereabout for a number of cycles before the return spring reasonance dissipates and the rotatable member comes to the complete rest at or proximate its normally stopped position. Utilization of this form of shock absorber also has the disadvantages that the shock absorber requires frequent adjustment to compensate for wear, its proper operation can be affected by weather conditions and its stroking characteristics, i.e., movement of a piston in a cylinder does not replicate the type of movement momentum it is absorbing , i.e., rotational movement. Further, if movement cycle frequency of the rotatable member is to be recorded and the said member can rotate through arcs of, e.g., 90.degree. at both sides of a normally stopped position datum, it is usually only possible to operate a counter when the member is rotating to one side of said datum and not the other. Further, oscillating movement of the rotatable component in many instances can cause miscounting or erroneous recording of the counter unit.
One form of mechanical device in which the foregoing disadvantages are particularly unsatisfactory is represented by rotatable spring loaded barriers used, for example, in connection with controlling and counting ingress and egress transit of humans at a given location and also for counting entry of automobiles to a parking facility. Such barriers should be quick acting particularly in return travel operation, as in the case of an automobile counter, so that the barrier is repositioned in normally stopped position to insure that counter actuating presentation thereof is available to meet a succeeding entering vehicle following closely behind a preceeding vehicle which has depressed the barrier. However, such quick acting return movement also should be effectively damped to stop the rotatively returning barrier without override of its normally stopped position to prevent "bounce" which can be annoying to customers and to some extent destructive of the barrier itself when such oscillations occur while in contact with an automobile.